Not usable in Greece, Peloponez
This time I bought unlimited data plan for Europe and using it in Bulgaria and Greece. For Bulgaria, it was ok, for Greece, it simply is not working, even in major places like Corinth and its surroundings. Unfortunately, my main target was Greece, since I was only transiting Bulgaria. It is so bad in Greece, that I am buying another eSim from local Cosmote operator in order to have some data plan.
